Conceptual precision is often regarded as a scholarly virtue by economists. This paper explores the scope and promise of definitionalism in economics by focusing on concepts that act as founding concepts in economic debate. The semantic properties of these founding concepts are investigated on the basis of a revised Fregean account of meaning, which reinterprets Fregean sense as a social object that determines meaning reflexively in an ethnographically grounded and non-determinist fashion. The resulting ‘finitist’ account of economic concepts casts doubt on the definitionalist project. What matters for founding concepts is less that they are well-defined, but that differences over their meaning do not prompt controversy.